In punching or stamping apparatuses a conveyor belt is used to convey the sheet-like good to be stamped to the stamping blade. The conveyor belt simultaneously also serves as the support or anvil during the stamping or punching of the sheet-like good or sheet material. Such conveyor belt is commonly designated as a “punching tape”. Such punching tape generally is shaped with the same components as an ordinary conveyor belt, but wherein the cover layer, acting as the support or anvil during the stamping or punching, is made of a highly wear-resistant material, usually polyurethane.
GB 1 311 622 discloses an apparatus for punching blanks using a punching belt constructed of three superposed layers of fabric and a coating of a wear-resistant material, such as nylon of a thickness of 3 mm, provided on the outer surface of the belt. These fabrics would have been understood by the skilled person as “woven” fabrics: FIG. 2 shows cross-sections of weft filaments in “fabrics 19 and 21” and cross-sections of warp filaments in “fabric 20”.
U.S. Pat. No. 5,699,707 discloses a cutting machine for cutting soft sheet material, comprising an endless micro-porous support belt 56 which overlies an endless endless conveyor 36 and which is made either of microporous sintered plastic beads or of a Fourdrinier cellulosic web saturated with latex. If the micro-porous support belt is made from sintered plastic beads it is devoid of any fibres. On the other hand, if it is made from a latex-saturated Fourdrinier cellulosic web, then the predominant component therein, such as 80-95 percent by weight, are cellulosic fibres, and the latex is a rubbery, thus crosslinked plastic.
GB 2 458 687 describes a rotary perforator or cutter for cutting or perforating paper. A rotating cylinder with perforating edges acts during cutting against an “anvil belt” which has a resilient surface which may e.g. be made of polyurethane, i.e. it is devoid of any fibers.
U.S. Pat. No. 6,233,989 describes an apparatus for stamping a metal sheet having a cushioning pad which is located between a supporting die and the metal sheet to be stamped. The cushioning pad is made of a compressible material. e.g. of vegetable or polymeric fibres, such as polyester, aramid and paper fibres being bound with a binder which may be a “nitrile” (i.e. nitrile rubber), “neoprene” (i.e. chloroprene rubber) or “SBR” (i.e. styrene-butadiene-rubber) binder, thus a crosslinked rubber. The stamping may be carried out either with cutting into the cushioning pad, or without cutting into the cushioning pad if an uncut pad is required for reuse.
U.S. Pat. No. 4,419,913 discloses a method and apparatus for cutting patterns in web material, wherein the web of pattern material rests upon a corresponding web of flexible material with a rough surface, such as a fleece, which permits passage of air and has vertical resilience. This web of flexible material is seemingly a neat fleece devoid of any plastic matrix.
The applicant marketed at the time of filing of this application belts comprising a traction layer and one or two impregnated nonwoven fabrics. An example of such belts had the type code UM220SC-B. This belt was indicated as suitable, among others, as a punching or stamping belt. The two impregnated nonwoven fabrics contain as the predominant component the fibres. Dedicated punching belts marketed by the applicant with type codes XVT-2197 and XVT-2249 on the other hand contained an impregnated woven polyamide fabric.
US 2004/168757 describes a monolithic belt of a thermoplastic material to which optionally elongated or fibre-formed additive materials, in unknown amounts, may be added to increase strength.
EP 0 638 414 mentions a process for the preparation of a thermoplastic substrate, in which an aqueous slurry of heat-fusible polymer particulates and reinforcing fibres is formed, the slurry is dewatered to form a dewatered mat, such as on a paper making machine, the dewatered mat is dried and then heat and pressure is applied to the dried mat to melt the thermoplastic resin. The amount of polymers in the composite substrate is 20-90%, preferably 30-70%. The amount of reinforcing material is generally 10-80% and preferably 30-70%.
Hard sheet materials consisting of a fibre-reinforced layer of a thermoplastic, customarily designated as “stampable sheets”, have been used for stamping and molding car parts in the automotive industry or printed circuit boards in the electronics industry. The molding and stamping are done at elevated temperature. For a description of such stampable sheets and their applications reference is made, by way of example, to U.S. Pat. No. 5,165,990.
U.S. Pat. No. 5,316,834 describes a two layered stampable sheet, consisting of a first layer of thermoplastic-impregnated woven or knitted fabric and a second layer of thermoplastic-impregnated nonwoven fabric. The fibres in the nonwoven fabric of the second layer are substantially uniformly distributed and the nonwoven fabric may be further needled, and may be e.g. a web of crimped meta-type aramid fibre to which a water jet needling has been applied. This stampable sheet can be molded at 250-300° C. into articles such as cylinders.
The present invention seeks to provide an improved sheet material suitable in a punching tape of the aforementioned type.